Decoding device, decoding method, and program

ABSTRACT

A decoding device includes an acquisition unit configured to acquire a first frequency signal including a narrowband signal and a wideband signal, a direct inverse orthogonal transform unit configured to perform a direct matrix operation with respect to the narrowband signal of the first frequency signal so as to perform inverse orthogonal transform, and a high-speed inverse orthogonal transform unit configured to perform inverse orthogonal transform employing a high-speed operation method with respect to the wideband signal of the first frequency signal.

BACKGROUND

The present technology relates to a decoding device, a decoding method,and a program. Especially, the present technology relates to a decodingdevice, a decoding method, and a program that can reduce an operationamount in inverse orthogonal transform with respect to a frequencysignal including a narrowband signal and a wideband signal.

In the related art, there is an encoding device that transforms a timesignal of a sound or the like into a frequency signal and quantizes thefrequency signal so as to encode and transmit the signal. Further, thereis a decoding device that decodes encoded data which is transmitted bysuch encoding device and inversely quantizes the data so as to transformthe resulting frequency signal into a time signal.

In such decoding device, inverse orthogonal transforms such as inversefast Fourier transform (IFFT), inverse discrete cosine transform (IDCT),and inverse modified discrete cosine transform (IMDCT) are often used asthe transform of a frequency signal into a time signal (referred tobelow as frequency-time transform).

On the other hand, there is a radio communication device that isprovided with a fast Fourier transform (FFT) having a predetermineddemodulation property and an FFT which has an inferior demodulationproperty but exhibits low power consumption and that switches and usesthese FFTs so as to suppress power consumption (For example, JapaneseUnexamined Patent Application Publication No. 2008-258992).

SUMMARY

In inverse orthogonal transform which is used in the frequency-timetransform described above, a matrix operation using spectra ofrespective divided bands constituting a frequency signal, as elements isperformed commonly by fast algorithm (fast operation method).Accordingly, when the frequency signal is a wideband signal, anoperation amount can be reduced compared to when a direct matrixoperation is performed.

However, when the frequency signal is a narrowband signal, a signal of adivided band which is larger than or equal to a predetermined bandbecomes a zero signal. Therefore, a redundant operation is performed,and thus the operation amount is increased compared to a case where adirect matrix operation is performed.

It is desirable to enable reduction of an operation amount in inverseorthogonal transform with respect to a frequency signal which includes anarrowband signal and a wideband signal.

According to an embodiment of the present technology, there is provideda decoding device that includes an acquisition unit configured toacquire a first frequency signal including a narrowband signal and awideband signal, a direct inverse orthogonal transform unit configuredto perform a direct matrix operation with respect to the narrowbandsignal of the first frequency signal so as to perform inverse orthogonaltransform, and a high-speed inverse orthogonal transform unit configuredto perform inverse orthogonal transform employing a high-speed operationmethod with respect to the wideband signal of the first frequencysignal.

A decoding method and a program according to embodiments of the presenttechnology correspond to the decoding device of the above-describedembodiment.

According to the embodiments, a first frequency signal including anarrowband signal and a wideband signal is acquired, a direct matrixoperation is performed with respect to the narrowband signal of thefirst frequency signal so as to perform inverse orthogonal transform,and inverse orthogonal transform employing a high-speed operation methodis performed with respect to the wideband signal of the first frequencysignal.

The decoding device according to the embodiment may be an independentdevice or an internal block constituting one device.

According to the embodiments of the present technology, an operationamount in inverse orthogonal transform with respect to a frequencysignal including a narrowband signal and a wideband signal can bereduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration example of a decodingdevice according to an embodiment of the present technology;

FIG. 2 illustrates a configuration example of encoded data transmittedto the decoding device of FIG. 1;

FIG. 3 illustrates an operation amount in DCT-IV in high-speed IMDCTperformed by an F/T converter in FIG. 1;

FIG. 4 illustrates an operation amount in DCT-IV in direct IMDCTperformed by an FIT converter in FIG. 1;

FIG. 5 is a graph showing the operation numbers in DCT-IV in high-speedIMDCT and direct IMDCT;

FIG. 6 is a flowchart of decoding processing performed by the decodingdevice of FIG. 1;

FIG. 7 is a block diagram showing a configuration example of a decodingdevice according to another embodiment of the present technology;

FIG. 8 illustrates a configuration example of encoded data transmittedto the decoding device of FIG. 7;

FIG. 9 is a flowchart of decoding processing performed by the decodingdevice of FIG. 7;

FIG. 10 is a block diagram showing a configuration example of a decodingdevice according to still another embodiment of the present technology;

FIG. 11 illustrates a configuration example of encoded data transmittedto the decoding device of FIG. 10;

FIG. 12 illustrates a using method of concealment data;

FIG. 13 is a flowchart of decoding processing performed by the decodingdevice of FIG. 10; and

FIG. 14 illustrates a configuration example of an embodiment of acomputer.

DETAILED DESCRIPTION OF EMBODIMENTS Embodiment

[Configuration Example of Decoding Device According to an Embodiment]

FIG. 1 is a block diagram showing a configuration example of a decodingdevice according to an embodiment of the present technology.

A decoding device 10 of FIG. 1 includes a DEMUX 11, a decoder 12, aninverse quantizer 13, a switch 14, an F/T converter 15, an F/T converter16, an output unit 17, and a controller 18. The decoding device 10decodes encoded data transmitted from an encoding device which is notshown. This encoded data is obtained by transforming a low frequencyeffect (LFE) signal such as a subwoofer signal serving as a narrowbandsignal and a common audio signal serving as a wideband signal intofrequency signals from time signals, and quantizing, encoding, andmultiplexing the frequency signals.

The DEMUX 11 (acquisition unit) of the decoding device 10 acquires theencoded data and inversely multiplexes the encoded data. Thus, the DEMUX11 extracts the frequency signal of the LFE signal which is quantizedand encoded, the frequency signal of the common audio signal which isquantized and encoded, and the like so as to supply the frequencysignals to the decoder 12. Further, the DEMUX 11 extracts a LFE flagwhich expresses whether an encoding result of the LFE signal is includedin the encoded data and supplies the LFE flag to the controller 18 andthe output unit 17.

The decoder 12 decodes the frequency signal of the LFE signal which isquantized and encoded and is supplied from the DEMUX 11 and supplies theresulting frequency signal of the LFE signal which is quantized to theinverse quantizer 13. Further, the decoder 12 decodes the frequencysignal of the common audio signal which is quantized and encoded and issupplied from the DEMUX 11 and supplies the resulting frequency signalof the common audio signal which is quantized to the inverse quantizer13.

The inverse quantizer 13 inversely quantizes the frequency signal of theLFE signal which is quantized and is supplied from the decoder 12 andsupplies the resulting frequency signal of the LFE signal to the switch14. Further, the inverse quantizer 13 inversely quantizes the frequencysignal of the common audio signal which is quantized and is suppliedfrom the decoder 12 and supplies the resulting frequency signal of thecommon audio signal to the switch 14.

The switch 14 (selecting unit) selects the frequency signal of thecommon audio signal among the frequency signals which are supplied fromthe inverse quantizer 13, based on an instruction supplied from thecontroller 18 and supplies the frequency signal of the common audiosignal to the FIT converter 15. Further, the switch 14 selects thefrequency signal of the LFE signal among the frequency signals which aresupplied from the inverse quantizer 13, based on an instruction suppliedfrom the controller 18 and supplies the frequency signal of the LFEsignal to the FIT converter 16.

The F/T converter 15 (high-speed inverse orthogonal transform unit)performs high-speed IMDCT with respect to the frequency signal of thecommon audio signal supplied from the switch 14 so as to obtain thecommon audio signal which is a time signal and supply the common audiosignal to the output unit 17. Here, the high-speed IMDCT representstransform employing a high-speed operation method in DCT-IV in IMDCT.

The F/T converter 16 (direct inverse orthogonal transform unit) performsdirect IMDCT with respect to the frequency signal of the LFE signalsupplied from the switch 14 so as to obtain the LFE signal which is atime signal and supply the LFE signal to the output unit 17. Here, thedirect IMDCT represents transform in which a direct matrix operation isperformed without using the high-speed operation method in DCT-IV inIMDCT. There is no significant difference between transformingcapability of the high-speed IMDCT and transforming capability of thedirect IMDCT.

The output unit 17 (output unit) generates a zero signal and outputs thezero signal as the LFE signal, or outputs the LFE signal supplied fromthe F/T converter 16 depending on a control of the controller 18.Further, the output unit 17 outputs the common audio signal suppliedfrom the F/T converter 15.

The controller 18 instructs the switch 14 to select either the F/Tconverter 15 or the F/T converter 16 based on a decoding object.Further, the controller 18 controls an output of the output unit 17based on the LFE flag supplied from the DEMUX 11.

[Configuration Example of Decoded Data]

FIG. 2 illustrates a configuration example of the encoded datatransmitted to the decoding device 10 of FIG. 1.

As shown in FIG. 2, a header, front LR (F-L,R), CENTER, LFE flag, LFE,and rear LR (R-L,R) are arranged from the head in this order in theencoded data.

The front LR is encoding results of common audio signals of two channelsfor the front right and the front left, and the encoding results of thetwo channels are arranged as one audio block. The CENTER is an encodingresult of a common audio signal of one channel for the center, and theencoding result of the one channel is arranged as one audio block.

The LFE flag becomes 1 when LFE is included in the encoded data andbecomes 0 when the LFE is not included. The LFE is an encoding result ofa LFE signal, and the encoding result is arranged as an audio blockdepending on necessity. The rear LR is encoding results of common audiosignals of two channels for the rear right and the rear left, and theencoding results of the two channels are arranged as one audio block.

Here, a block ID, which is different for every kind of signalsconstituting the audio block, is added to each of the audio blocks.Namely, different block IDs are added to respective audio blocks of thefront LR, the CENTER, the LFE, and the rear LR respectively. In thisexample, block IDs “1”, “2”, “3”, and “4” are respectively added to theaudio blocks of the front LR, the CENTER, the LFE, and the rear LR.

[Description of Operation Amount in High-Speed IMDCT and Direct IMDCT]

FIG. 3 illustrates an operation amount in DCT-IV in the high-speed IMDCTperformed by the F/T converter 15 of FIG. 1, and FIG. 4 illustrates anoperation amount in DCT-IV in the direct IMDCT performed by the F/Tconverter 16 of FIG. 1.

DCT-IV in IMDCT is first described.

IMDCT indicates transform which is performed while duplicating blocks bymaking the number of taps twice as large as the division number, and canreduce distortion between the blocks. In DCT-IV in IMDCT, multiplicationis performed with respect to the frequency signal which is an inputsignal, as shown in the following Formula 1.

$\begin{matrix}{\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{N}\end{bmatrix} = {\lbrack C_{N}^{4} \rbrack \cdot \begin{bmatrix}X_{1} \\X_{2} \\\vdots \\X_{N}\end{bmatrix}}} & (1)\end{matrix}$

In Formula 1, N denotes the number of band divisions of the frequencysignal which is an input signal, and X_(N) denotes a spectrum of then-th division band. C_(N) ⁴ denotes a transform matrix of DCT-IV, andy_(N) denotes a signal of the spectrum of the n-th division band aftertransform.

In the high-speed IMDCT with respect to the common audio signal by theF/T converter 15, a high-speed operation method is employed as anoperation method of such DCT-IV. Several methods are proposed as thehigh-speed operation method, including Wang algorithm as one of themethods. The Wang algorithm realizes speed-up of the operation bydecomposing a DCT matrix into a sparse matrix which includes largenumber of zero elements. FIG. 3 shows the operation amount of DCT-IVwhen the Wang algorithm is employed.

Specifically, as shown in FIG. 3, the number of times of multiplicationDCT-IV is N(log₂N+1), and the number of times of addition is N(3log₂N−1)/2. The number of times of reading which is the number ofreading out a spectrum X_(N) from a built-in memory which is not shownis N log₂N, and the number of times of evacuation which is the number ofevacuating an intermediate result to the built-in memory which is notshown is N log₂N.

Accordingly, when N is 256(log₂N=8), for example, the number of times ofmultiplication becomes 2304, the number of times of addition becomes244, and the number of times of reading and the number of times ofevacuation become 2048.

On the other hand, the LFE signal is commonly a signal having anultralow frequency about 0 Hz to 120 Hz. Accordingly, as shown in thefollowing Formula 2, the number of spectra X_(N) in a valid band, thatis, the number of valid division bands becomes M (M<N), and the spectraX_(N) in other division bands of M−N pieces becomes 0.X=[X₁,X₂, . . . X_(M),0, . . . ,0]^(T)  (2)

For example, when the frequency of the common audio signal is 48 kHz, anavailable band of the common audio signal is 24 kHz. Therefore, if thenumber of band divisions is 256, the number of spectra of the LFE signalof 120 Hz becomes 1.28 (=120×256/24000), and thus M has a valuesufficiently smaller than the value of N.

In the direct IMDCT with respect to the LFE signal performed by the F/Tconverter 16, the high-speed operation method is not employed as theoperation method of DCT-IV, but the direct matrix operation is performedby employing the following Formula 3.

$\begin{matrix}{\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\\vdots \\\vdots \\y_{N - 1} \\y_{N}\end{bmatrix} = {\quad{\begin{bmatrix}C_{11} & C_{12} & \ldots & C_{1\; M} & \ldots & C_{1{({N - 1})}} & C_{1\; N} \\C_{21} & C_{22} & \ldots & C_{2\; M} & \ldots & C_{2{({N - 1})}} & C_{2\; N} \\\vdots & \vdots & \ldots & \vdots & \ldots & \vdots & \vdots \\\vdots & \vdots & \ldots & \vdots & \ldots & \vdots & \vdots \\\vdots & \vdots & \ldots & \vdots & \ldots & \vdots & \vdots \\C_{{({N - 1})}1} & C_{{({N - 1})}2} & \ldots & C_{{({N - 1})}M} & \ldots & C_{{({N - 1})}{({N - 1})}} & C_{{({N - 1})}N} \\C_{N\; 1} & C_{N\; 2} & \ldots & C_{NM} & \ldots & C_{N{({N - 1})}} & C_{NN}\end{bmatrix}\begin{bmatrix}X_{1} \\X_{2} \\\vdots \\X_{M} \\0 \\\vdots \\0\end{bmatrix}}}} & (3)\end{matrix}$

In Formula 3, C₁₁ to C_(NN) denote respective elements of a transformmatrix C_(N) ⁴, that is, transform coefficients.

According to Formula 3, spectra X_(M+1) to X_(N) which are the M+1th andlater division bands are all 0, so that no operation has to be performedwith respect to the spectra X_(M+1) to X_(N). Accordingly, the operationamount in DCT-IV in the direct IMDCT with respect to the LFE signalbecomes as shown in FIG. 4.

Specifically, as shown in FIG. 4, the numbers of times ofmultiplication, addition, and reading in DCT-IV are N×M, and the numberof times of evacuation is N.

FIG. 5 is a graph showing the number of operations in DCT-IV in thehigh-speed IMDCT when the number of band divisions is 256 and the numberof operations in DCT-IV in the direct IMDCT.

In FIG. 5, the number of operations indicates the number obtained byadding the number of times of multiplication, the number of times ofaddition, the number of times of reading, and the number of times ofevacuation. Further, in FIG. 5, the horizontal axis represents thenumber of valid elements in the matrix operation of DCT-IV, that is, thenumber M of valid spectra X_(N), and the vertical axis represents thenumber of operations. Furthermore, in FIG. 5, a solid line denotes thenumber of operations in DCT-IV in the high-speed IMDCT and a dashed linedenotes the number of operations in DCT-IV in the direct IMDCT.

According to the graph shown in FIG. 5, when M is equal to less than 11,the number of operations in DCT-IV in the direct IMDCT is lower than thenumber of operations in DCT-IV in the high-speed IMDCT. That is, when Mis equal to or less than 11, the operation amount in performing thedirect IMDCT with respect to a frequency signal is smaller than that inperforming the high-speed IMDCT.

Thus, when M is sufficiently small, the operation amount in performingthe direct IMDCT with respect to a frequency signal is smaller than thatin performing the high-speed IMDCT. Accordingly, in the decoding device10, the F/T converter 15 performs the high-speed IMDCT with respect to acommon audio signal, and the F/T converter 16 performs the direct IMDCTwith respect to a LFE signal of which M is sufficiently small. As aresult, the operation amount of the frequency-time transform can bereduced and the power consumption can be reduced.

[Description of Processing of Decoding Device]

FIG. 6 is a flowchart of decoding processing performed by the decodingdevice 10 of FIG. 1. The decoding processing is started when encodeddata is inputted into the decoding device 10, for example.

In step S11, the controller 18 sets an objective block ID iblk, which isa block ID of an audio block which is an object of the processing, inthe encoded data to be 0.

In step S12, the DEMUX 11 determines whether the objective block ID iblkis block ID iblk_lfe of the LFE, that is, whether the objective block IDiblk is 2. When it is determined that the objective block ID iblk is notthe block ID iblk_lfe of the LFE in step S12, the processing goes tostep S14.

On the other hand, when it is determined that the objective block IDiblk is the block ID iblk_lfe of the LFE in step S12, the controller 18determines whether the LFE flag supplied from the DEMUX 11 is 1 in stepS13. This LFE flag is obtained by inversely multiplexing the encodeddata by the DEMUX 11.

When it is determined that the LFE flag is 1 in step S13, that is, whenan encoding result of the LFE is included in the encoded data, thecontroller 18 instructs the output unit 17 to output a time signal fromthe F/T converter 16. Then, the processing goes to step S14.

In step S14, the DEMUX 11 inversely multiplexes the encoded data,extracts an audio block of the objective block ID iblk, and supplies theextracted audio block to the decoder 12.

In step S15, the decoder 12 decodes the audio block supplied from theDEMUX 11 and supplies the resulting frequency signal which is quantizedto the inverse quantizer 13.

In step S16, the inverse quantizer 13 inversely quantizes the frequencysignal which is quantized and is supplied from the decoder 12 andsupplies the resulting frequency signal to the switch 14.

In step S17, the controller 18 determines whether the objective block IDiblk is the block ID iblk_lfe of the LFE. When it is determined that theobjective block ID iblk is not the block ID iblk_lfe of the LFE in stepS17, the controller 18 instructs the switch 14 to select the F/Tconverter 15. The switch 14 supplies the frequency signal supplied fromthe inverse quantizer 13, that is, a frequency signal corresponding tofront LR, CENTER, or rear LR, to the F/T converter 15, in response tothe instruction.

In step S18, the F/T converter 15 performs the high-speed IMDCT withrespect to the frequency signal supplied from the switch 14 and outputsthe resulting time signal via the output unit 17. Then, the processinggoes to step S21.

On the other hand, when it is determined that the objective block IDiblk is the block ID iblk_lfe of the LFE in step S17, the controller 18instructs the switch 14 to select the F/T converter 16. The switch 14supplies the frequency signal supplied from the inverse quantizer 13,that is, the frequency signal of the LFE signal to the F/T converter 16in response to the instruction.

In step S19, the F/T converter 16 performs the direct IMDCT with respectto the frequency signal of the LFE supplied from the switch 14 andoutputs the resulting time signal via the output unit 17. Then, theprocessing goes to step S21.

On the other hand, when it is determined that the LFE flag is not 1 instep S13, that is, when the audio block of the LFE is not included inthe encoded data, the controller 18 instructs the output unit 17 tooutput a zero signal. Then, the processing goes to step S20.

In step S20, the output unit 17 generates a zero signal in response tothe instruction of the controller 18 and outputs the zero signal as theLFE signal. Then, the processing goes to step S21.

In step S21, the DEMUX 11 increments the objective block ID iblk by 1,and the processing goes to step S22.

In step S22, the DEMUX 11 determines whether the objective block ID iblkis a total number nblks of kinds of audio blocks, that is, whether theobjective block ID iblk is 4. When it is determined that the objectiveblock ID iblk is not the total number nblks in step S22, the processingreturns to step S12 and processing of steps S12 to S22 is repeated untilthe objective block ID iblk becomes the total number nblks.

When it is determined that the objective block ID iblk is the totalnumber nblks in step S22, that is, when all audio blocks are the objectof the processing, the processing is ended.

Another Embodiment

[Configuration Example of Decoding Device According to AnotherEmbodiment]

FIG. 7 is a block diagram showing a configuration example of a decodingdevice according another embodiment of the present technology.

In the configuration shown in FIG. 7, elements same as those of theconfiguration of FIG. 1 are given the same reference numerals. Redundantdescription is arbitrarily omitted.

A decoding device 30 shown in FIG. 7 has the configuration differentfrom that of FIG. 1 in the way that the decoding device 30 includes aDEMUX 31 and a controller 32 instead respectively of the DEMUX 11 andthe controller 18 and does not include the output unit 17. The decodingdevice 30 decodes encoded data which does not include a LFE flag butconstantly includes an encoding result of LFE.

Specifically, in the decoding device 30, the DEMUX 31 acquires encodeddata and inversely multiplexes the encoded data. Accordingly, the DEMUX31 extracts audio blocks of front LR, CENTER, and rear LR which arefrequency signals of a common audio signal which is quantized andencoded and supplies the audio blocks to the decoder 12. Further, theDEMUX 31 extracts an audio block of LFE which is a frequency signal of aLFE signal which is quantized and encoded and supplies the audio blockto the decoder 12.

The controller 32 instructs the switch 14 to select either F/T converter15 or the F/T converter 16 based on a decoding object.

[Configuration Example of Coded Data]

FIG. 8 illustrates a configuration example of the encoded datatransmitted to the decoding device 30 of FIG. 7.

In the encoded data of FIG. 8, a header, front LR, CENTER, LFE, and rearLR are arranged from the head in this order. In the encoded data of FIG.8, the audio block of the LFE is constantly arranged, being differentfrom the encoded data of FIG. 2. Accordingly, a LFE flag is not arrangedin the encoded data of FIG. 8.

[Description of Processing of Decoding Device]

FIG. 9 is a flowchart of decoding processing performed by the decodingdevice 30 of FIG. 7. This decoding processing is started when encodeddata is inputted into the decoding device 30, for example.

The decoding processing of FIG. 9 is processing which does not includesteps S12, S13, and S20 of the decoding processing of FIG. 6. That is,processing from step S31 to step S39 of FIG. 9 are same as steps S11,S14 to S19, S21, and S22 of FIG. 6. Therefore, the description thereofis omitted.

Here, in the embodiments described first and second, a supplydestination of the switch 14 is changed based on the block ID of adecoding object. However, the supply destination of the switch 14 may bechanged based on an arrangement order of respective audio blocks in theencoded data. In this case, when LFE is included and the third audioblock from the head of the encoded data is the decoding object, the F/Tconverter 16 is selected as the supply destination, and when other audioblocks are the decoding object, the F/T converter 15 is selected as thesupply destination.

Still Another Embodiment

[Configuration Example of Decoding Device of Still Another Embodiment]

FIG. 10 is a block diagram showing a configuration example of a decodingdevice according to still another embodiment of the present technology.

A decoding device 50 of FIG. 10 includes a DEMUX 51, a decoder 52, aninverse quantizer 53, a switch 54, a F/T converter 55, a F/T converter56, and a memory 57. The decoding device 50 decodes encoded dataincluding actual data which is an encoding result of an original audiosignal and concealment data which is an encoding result of a concealmentsignal which is used instead of the original audio signal when an errorcaused by a transmission channel or the like occurs in the actual data.Here, as the concealment signal, a signal of a band narrower than thatof the original audio signal is used.

In the decoding device 50, the DEMUX 51 acquires encoded data andinversely multiples the encoded data. Accordingly, the DEMUX 51 extractsactual data and concealment data. Then, when no error occurs in inversemultiplexing, the DEMUX 51 supplies the actual data and the concealmentdata respectively to the decoder 52 and the memory 57. Further, theDEMUX 51 supplies an error flag showing whether an error occurs to thedecoder 52 depending on presence/absence of an occurrence of an error ininverse multiplexing.

When the error flag from the DEMUX 51 shows that no error occurs, thedecoder 52 decodes the actual data supplied from the DEMUR 51. When noerror occurs in decoding, the decoder 52 supplies a frequency signal ofan original audio signal which is quantized and obtained as a result ofencoding to the inverse quantizer 53, and instructs the memory 57 torecord the concealment data.

On the other hand, when the error flag from the DEMUX 51 shows that anerror occurs, or when an error occurs in decoding the actual data, thedecoder 52 reads out the concealment data from the memory 57. Then, thedecoder 52 decodes the concealment data and supplies the resultingfrequency signal of the concealment signal which is quantized to theinverse quantizer 53. Further, the decoder 52 supplies an error flag tothe switch 54 based on the presence/absence of an error in decoding andthe error flag supplied from the DEMUX 51.

The inverse quantizer 53 inversely quantizes the frequency signal of theoriginal audio signal or the frequency signal of the concealment signalwhich are quantized and supplied from the decoder 52, and supplies theresulting frequency signal of the original audio signal or theconcealment signal to the switch 54.

When an error flag showing no occurrence of an error is supplied fromthe decoder 52, the switch 54 supplies the frequency signal suppliedfrom the inverse quantizer 53 to the F/T converter 55. That is, when thefrequency signal of the original audio signal is supplied from theinverse quantizer 53, the frequency signal is supplied to the F/Tconverter 55.

On the other hand, when an error flag showing an occurrence of an erroris supplied from the decoder 52, the switch 54 supplies the frequencysignal supplied from the inverse quantizer 53 to the F/T converter 56.That is, when the frequency signal of the concealment signal is suppliedfrom the inverse quantizer 53, the frequency signal is supplied to theF/T converter 56.

The F/T converter 55 performs high-speed IMDCT with respect to thefrequency signal of the original audio signal which is supplied from theswitch 54 so as to obtain the original audio signal which is a timesignal and output the original audio signal.

The F/T converter 56 performs direct IMDCT with respect to the frequencysignal of the concealment signal which is supplied from the switch 54 soas to obtain the concealment signal which is a time signal and outputthe concealment signal.

The memory 57 records the concealment data supplied from the DEMUX 51 inresponse to the instruction of the encoder 52.

[Configuration Example of Encoded Data]

FIG. 11 illustrates a configuration example of the encoded datatransmitted to the decoding device 50 of FIG. 10.

In the encoded data of FIG. 11, a header, actual data, and concealmentdata of each frame are arranged from the head in this order. Theconcealment data of each frame is an encoding result of a frequencysignal of a narrow band of actual data of the frame, for example. Actualdata and concealment data included in the same encoded data correspondto different frames respectively. Specifically, encoded data of acertain frame includes actual data of the frame and concealment data ofthe following frame.

[Description of Using Method of Concealment Data]

FIG. 12 illustrates a using method of concealment data.

As shown in FIG. 12, encoded data [n−1] which is encoded data of then−1th frame includes actual data [n−1] which is actual data of the n−1thframe and concealment data [n] which is concealment data of the nthframe.

In the same manner, encoded data [n] which is encoded data of the nthframe includes actual data [n] which is actual data of the nth frame andconcealment data [n+1] which is concealment data of the n+1th frame.Encoded data [n+1] which is encoded data of the n+1th frame includesactual data [n+1] which is actual data of the n+1th frame andconcealment data [n+2] which is concealment data of the n+2th frame.

Here, when no error occurs in the encoded data of the n−1th frame and anerror occurs in the encoded data of the nth frame, the decoder 52decodes the concealment data [n] which is included in the encoded dataof the n−1th frame, which is one frame before the encoded data of thenth frame, instead of the actual data [n]. As a result, loss and damageof the actual data can be concealed and sound interruption can beprevented.

Further, actual data and concealment data of different frames areincluded in the same encoded data, so that simultaneous loss of actualdata and concealment data of the same frame can be prevented.

[Description of Processing of Decoding Device]

FIG. 13 is a flowchart of decoding processing performed by the decodingdevice 50 of FIG. 10. The decoding processing is started when encodeddata is inputted into the decoding device 50, for example.

In step S51, the DEMUX 51 inversely multiplexes the encoded data.Accordingly, the DEMUX 51 extracts actual data and concealment data.

In step S52, the DEMUX 51 determines whether an error occurs in inversemultiplexing. When it is determined that no error occurs in inversemultiplexing in step S52, the decoder 52 decodes actual data suppliedfrom the DEMUX 51 in step S53.

In step S54, the decoder 52 determines whether an error occurs indecoding. When it is determined that no error occurs in decoding in stepS54, the decoder 52 instructs the memory 57 to record the concealmentdata.

In step S55, the memory 57 records the concealment data supplied fromthe DEMUX 51 in response to the instruction of the decoder 52.

In step S56, the decoder 52 sets an error flag (errFlag) to be 0 whichexpresses no occurrence of an error and supplies the error flag to theswitch 54. Then, the processing goes to step S61.

On the other hand, when it is determined that an error occurs in inversemultiplexing in step S52, the DEMUX 51 sets the error flag to be 1 whichexpresses an occurrence of an error and supplies the error flag to thedecoder 52 in step S57. Then, the processing goes to step S58.

Further, when it is determined that an error occurs in decoding in stepS54, the processing goes to step S58.

In step S58, the decoder 52 reads out the concealment data from thememory 57. In step S59, the decoder 52 decodes the concealment data readout from the memory 57 and supplies the frequency signal of theconcealment signal which is quantized to the inverse quantizer 53.

In step S60, the decoder 52 sets the error flag to be 1 and supplies theerror flag to the switch 54. Then, the processing goes to step S61.

Step S61, the inverse quantizer 53 inversely quantizes a frequencysignal of an original audio signal or a frequency signal of theconcealment signal which are quantized and supplied from the decoder 52and supplies the resulting frequency signal of the original audio signalor the resulting frequency signal of the concealment signal to theswitch 54.

In step S62, the switch 54 determines whether the error flag suppliedfrom the decoder 52 is 1. When it is determined that the error flag isnot 1 in step S62, that is, when the error flag is 0, the switch 54supplies the frequency signal of the original audio signal which is thefrequency signal supplied from the inverse quantizer 53 to the F/Tconverter 55. Then, the processing goes to step S63.

In step S63, the F/T converter 55 performs high-speed IMDCT with respectto the frequency signal of the original audio signal which is suppliedfrom the switch 54 and outputs the resulting time signal. Then, theprocessing is ended.

On the other hand, when it is determined that the error flag is 1 instep S62, that is, when an error occurs in at least one of the DEMUX 51and the decoder 52, the switch 54 supplies the frequency signal of theconcealment signal which is the frequency signal supplied from theinverse quantizer 53 to the F/T converter 56.

Then, in step S64, the F/T converter 56 performs direct IMDCT withrespect to the frequency signal of the concealment signal supplied fromthe switch 54 and outputs the resulting time signal. Then, theprocessing is ended.

Yet Another Embodiment

[Description of Computer to which Embodiments of the Present Technologyare Applied]

The series of the processing described above may be performed either byhardware or software. In a case where the series of processing isperformed by software, a program constituting the software is installedinto a general-purpose computer or the like.

FIG. 14 illustrates a configuration example of an embodiment of acomputer on which a program which performs the above-described series ofprocessing is installed.

The program can be preliminarily stored in a storage unit 208 or a readonly memory (ROM) 202 which serves as a storage medium built in thecomputer.

Alternatively, the program can be stored (recorded) in a removablemedium 211. Such the removable medium 211 can be provided as so-calledpackaged software. Here, examples of the removable medium 211 include aflexible disc, a compact disc read only memory (CD-ROM), a magnetooptical (MO) disc, a digital versatile disc (DVD), a magnetic disc, anda semiconductor memory.

The program can be installed on the computer from the removable medium211 described above through a drive 210, or the program can bedownloaded into the computer through a communication network or abroadcast network so as to be installed on the storage unit 208 which isbuilt in. That is, the program can be wirelessly transferred to thecomputer from a download site through a satellite for digital satellitebroadcast or can be transferred in a wired fashion through a networksuch as a local area network (LAN) and an internet, for example.

The computer includes a central processing unit (CPU) 201 built in, andan input-output interface 205 is connected to the CPU 201 through a bus204.

When an input unit 206 is operated, for example, by a user and thus acommand is inputted into the CPU 201 through the input-output interface205, the CPU 201 executes the program stored in the ROM 202 inaccordance with the command. Alternatively, the CPU 201 loads theprogram stored in the storage unit 208 into a random access memory (RAM)203 so as to execute the program.

Accordingly, the CPU 201 performs processing following theabove-described flowchart or processing performed by the structure ofthe above-described block diagram. Then, the CPU 201, for example,outputs the processing result from an output unit 207, transmits theprocessing result from a communication unit 209, or allows the storageunit 208 to store the processing result through the input-outputinterface 205, as necessary.

The input unit 206 is a key board, a mouse, a microphone, or the like.The output unit 207 is a liquid crystal display (LCD), a speaker, or thelike.

In this specification, the processing performed by the computer inaccordance with the program is not necessarily performed in atime-series manner following the order described as the flowchart. Thatis, the processing performed by the computer in accordance with theprogram includes processing performed in a parallel manner or in anindividual manner (for example, parallel processing or processing by anobject), as well.

The program may be processed by a single computer (processor) or may beprocessed in a distributed manner by a plurality of computers. Further,the program may be transferred to a remote computer and be performed.

The embodiments of the present technology are applicable not only to adecoding device which performs IMDCT as frequency-time transform butalso to a decoding device which performs other inverse orthogonaltransform such as IFFT and IDCT.

Further, the embodiments of the present technology are applicable to adecoding device which decodes encoded data of a signal other than anaudio signal.

It should be understood that embodiments of the present technology arenot limited to the embodiments described above and various alterationsmay occur within the scope of the present technology.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2010-173943 filed in theJapan Patent Office on Aug. 2, 2010, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A decoding device, comprising: an acquisitionunit configured to acquire a first frequency signal including anarrowband signal and a wideband signal; a direct inverse orthogonaltransform unit configured to perform a direct matrix operation withrespect to the narrowband signal of the first frequency signal so as toperform inverse orthogonal transform; and a high-speed inverseorthogonal transform unit configured to perform inverse orthogonaltransform employing a high-speed operation method with respect to thewideband signal of the first frequency signal.
 2. The decoding deviceaccording to claim 1, further comprising: a selecting unit that selectsthe narrowband signal of the first frequency signal so as to supply thenarrowband signal to the direct inverse orthogonal transform unit andselects the wideband signal so as to supply the wideband signal to thehigh-speed inverse orthogonal transform unit; wherein informationexpressing being the narrowband signal is added to the narrowband signaland information expressing being the wideband signal is added to thewideband signal, and the selecting unit selects the narrowband signaland the wideband signal based on the information.
 3. The decoding deviceaccording to claim 1, further comprising: a selecting unit that selectsthe narrowband signal of the first frequency signal so as to supply thenarrowband signal to the direct inverse orthogonal transform unit andselects the wideband signal so as to supply the wideband signal to thehigh-speed inverse orthogonal transform unit; wherein the narrowbandsignal and the wideband signal are arranged in a predetermined order inthe first frequency signal, and the selecting unit selects thenarrowband signal and the wideband signal based on the order in thefirst frequency signal.
 4. The decoding device according to claim 1,further comprising: an output unit configured to generate a zero signaland output the zero signal; wherein the acquisition unit furtheracquires a second frequency signal that includes no narrowband signalbut includes the wideband signal, and the output unit outputs the zerosignal as a result of inverse orthogonal transform of the narrowbandsignal of the second frequency signal.
 5. The decoding device accordingto claim 4, wherein information expressing inclusion of the narrowbandsignal is added to the first frequency signal, information expressing noinclusion of the narrowband signal is added to the second frequencysignal, and the output unit outputs the zero signal as a result ofinverse orthogonal transform of the narrowband signal of the secondfrequency signal based on the information.
 6. The decoding deviceaccording to claim 1, wherein the narrowband signal is a low frequencyeffect signal, and the wideband signal is a wideband audio signal. 7.The decoding device according to claim 1, wherein the narrowband signalis a concealment signal that is used when an error occurs in thewideband signal.
 8. The decoding device according to claim 7, whereinwhen an error occurs in the wideband signal, the direct inverseorthogonal transform unit performs the direct matrix operation withrespect to the narrowband signal so as to perform the inverse orthogonaltransform, and outputs a resulting time signal as a time signal of thewideband signal, and when no error occurs in the wideband signal, thehigh-speed inverse orthogonal transform unit performs the inverseorthogonal transform employing the high-speed operation method withrespect to the wideband signal and outputs the resulting signal.
 9. Thedecoding device according to claim 1, wherein the inverse orthogonaltransform performed by the direct inverse orthogonal transform unitincludes a product sum operation of a spectrum in a valid band of thenarrowband signal and a predetermined coefficient.
 10. A decoding methodthat is employed by a decoding device, comprising: performing a directmatrix operation with respect to a narrowband signal of a frequencysignal that includes the narrowband signal and a wideband signal so asto perform inverse orthogonal transform; and performing inverseorthogonal transform employing a high-speed operation method withrespect to the wideband signal of the frequency signal.
 11. Anon-transitory computer-readable medium storing a program which, whenexecuted by a computer, causes the computer to perform processingcomprising: performing a direct matrix operation with respect to anarrowband signal of a frequency signal that includes the narrowbandsignal and a wideband signal so as to perform inverse orthogonaltransform; and performing inverse orthogonal transform employing ahigh-speed operation method with respect to the wideband signal of thefrequency signal.